Such devices are said to be "hand-held" in that they can be held in the hand: they are generally actuated by pressing a finger on the pushbutton, but they may be actuated by mechanical means or electromechanical means. Such devices are generally discarded after their supply of substance has been used up, and as a result they must be cheap.
There exists a large number of pushbuttons in the state of the art suitable for actuating a spray or a dispenser, which buttons fit onto an outlet tube of a spray or a dispenser and include an outlet orifice for the substance. Such pushbuttons are generally of fixed shape such that the rate at which substance flows through them depends solely on the pressure of said substance in the outlet tube of the spray or dispenser. Thus, a user cannot adjust the outlet flow rate of the substance as desired so that the substance is delivered drop by drop or on the contrary in the form of a powerful jet.
This function of being able to adjust the outlet flow rate of the substance is particularly necessary for devices using nitrogen as a propellant. It is known that, unlike freons, nitrogen under ordinary pressures does not liquefy to mix with the substance contained in the supply in the device: nitrogen pressure is thus high when the receptacle is nearly full of substance, and then the nitrogen expands as the substance is consumed so the nitrogen pressure falls off. When using a conventional pushbutton of fixed shape on such a device having nitrogen as its propellant, the delivery flow rate of the substance is thus high when the receptacle of substance is full, and this flow rate drops off as the pressure of the nitrogen itself drops off as the substance is consumed. There is thus a danger of the flow rate of the substance being too high initially and/or too low when the receptacle of substance is nearly empty.
It is therefore clearly desirable to provide a pushbutton enabling a user to adjust the outlet flow rate of the substance to that which may be required the purpose of the adjustment may either be to vary the flow rate of the substance or else on the contrary it may be to maintain it within a range of acceptable values, as described above. Such an improvement should be achieved without significantly increasing the cost of the pushbutton relative to a conventional pushbutton of fixed shape.
It is also useful to be able to close the outlet orifice of a pushbutton while it is not in use to prevent the substance contained in the pushbutton drying out, to prevent it oxidizing, or to prevent it being polluted on contact with the air.